Working at a pharmacy in Dessau, he made the acquaintance of the police director Brueckner who introduced him to the founder of the zoological museum in Leipzig, Professor Eduard Friedrich Pöppig.
Gueinzius settled on the Tugela River and supplied the medical needs of the Zulu chief Mpande (Dingaan's half-brother) and his wives.
Returning from an expedition to the north, he found that armed conflict had erupted between the English, Boers and Zulus, and that his home had been plundered by British troops.
He stayed at first with a friend, Campion, and found that almost all the Boer families he had known earlier, had left Natal and gone north to escape British dominion.
He leads an ingenious hermit life, very lonesome in the forest among the birds, and four-footed and crawling animals with which he has an affinity.
In addition to specimens of flowering plants, he collected marine algae, mosses and ferns, as well as bats, snakes and insects.
He died at Grey's Hospital in Pietermaritzburg, shortly before he was due to return to Germany to live with his brother Karl August Gueinzius in the Province of Saxony.